1. Field of the Invention
The present invention relates to a structural member for constructing a vehicle body, and more particularly, to a channel member for constructing a part of a vehicle body to provide an elongated wall portion thereof.
2. Description of the Prior Art
The body of a vehicle such as an automobile includes an elongated wall portion like the center pillar between the front and rear doors. The vehicle body is required to be as light as possible, while maintaining a required integrity of the body construction under a design load imposed thereon. In view of this, it was a conventional art that such an elongated wall portion is constructed by a channel member.
FIG. 1 shows a general construction of the center pillar of a four-wheeled automobile in a perspective view, while FIGS. 2 and 3 show two typical cross sectional constructions of such a center pillar. As depicted in these figures, the center pillar generally designated by 10 is assembled of a channel member 12 cast from, for example, an aluminum alloy or a magnesium alloy, and a cover member 14, also generally channel-shaped but essentially an outside decoration member bearing no substantial load because of its reduced thickness, press-formed from, for example, also an aluminum alloy or a magnesium alloy.
In the construction shown in FIG. 2, the channel member generally designated by 12 includes a bottom wall portion 12A extending substantially in parallel with the direction of transverse extension of the elongated wall portion (center pillar) of the vehicle body (i.e. the longitudinal direction of the vehicle body) as viewed in the cross section of the channel member, a pair of side wall portions 12B connected with the bottom wall portion 12A along adjacent ends thereof and extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, and a pair of flange portions 12C connected with the side wall portions 12B along adjacent ends thereof and extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member. A pair of rib portions 12D are provided as connected to the bottom wall portion 12A to extend substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member.
On the other hand, the cover member generally designated by 14 includes a roof wall portion 14A extending substantially in parallel with the direction of transverse extension of the elongated wall portion of the vehicle body as viewed in the cross section of the cover member, a pair of side wall portions 14B connected with the roof wall portion 14A along adjacent ends thereof and extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the cover member, and a pair of flange portions 14C connected with the side wall portions 14B along adjacent ends thereof and extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the cover member.
The channel member 12 and the cover member 14 are assembled together by the respective pairs of flange portions 12C and 14C being connected with one another by some spot welding.
In the construction shown in FIG. 3, the channel member 12xe2x80x2 is different from that shown in FIG. 2 in the position of concavity thereof such that the bottom wall portion 12A in FIG. 2 is changed to a roof wall portion 12Axe2x80x2, with an accompanying change of direction of extension of the pair of side wall portions 12B to that of a pair of side wall portions 12Bxe2x80x2. A pair of flange portions 12C are substantially the same as in FIG. 2. In FIG. 3, other portions corresponding to those shown in FIG. 2 are designated by the same reference numerals as in FIG. 2.
In an elongated wall portion of a vehicle body such as the center pillar of a four-wheeled automobile, it is probable that an accidental side force is applied thereto at right angle to its elongation as shown by an arrow Fs in FIG. 1, tending to bend the elongated wall portion about a neutral axis of its cross section extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section. When it occurs, when the elongated wall portion is constructed by a relatively shallow channel member such as shown in FIGS. 2 or 3 for the convenience of design of the vehicle body, with the bottom or roof wall portion 12A or 12Axe2x80x2 being extended substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, a bending moment generated by the accidental side force Fs must be reacted by a smallest geometrical moment of inertia of the cross section, i.e. a weakest bending strength of the channel member.
In view of the above-mentioned accidental probability of a side force acting at right angle to an elongated wall portion of a vehicle body constructed by a channel member and the weakness of the channel member against the side force acting substantially perpendicularly to the bottom or roof wall portion thereof, it is a primary object of the present invention to propose a channel member for constructing a part of a vehicle body to provide an elongated wall portion thereof such that the channel member has an improved strength against such a side force.
According to the present invention, the above-mentioned primary object is accomplished by a channel member for constructing a part of a vehicle body to provide an elongated wall portion thereof, comprising:
a first side wall portion extending substantially perpendicularly to a direction of transverse extension of the elongated wall portion as viewed in a cross section of the channel member, so as to define a first side of the channel member;
a second side wall portion extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, so as to define a second side of the channel member opposite to the first side;
a first bottom wall portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the first bottom wall portion being connected with the first side wall portion along adjacent ends thereof;
a second bottom wall portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the second bottom wall portion being connected with the second side wall portion along adjacent ends thereof;
a first perpendicular intermediate wall portion extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the first perpendicular intermediate wall portion being connected with the first bottom wall portion along adjacent ends thereof, so as to define a first sub-channel portion together with the first side wall portion and the first bottom wall portion;
a second perpendicular intermediate wall portion extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the second perpendicular intermediate wall portion being connected with the second bottom wall portion along adjacent ends thereof, so as to define a second sub-channel portion together with the second side wall portion and the second bottom wall portion; and
a central wall portion extending between the first and second perpendicular intermediate wall portions, the central wall portion being connected with the first and second perpendicular intermediate wall portions along adjacent ends thereof, so as to integrally connect the first and second sub-channel portions with one another.
The strength of a conventional channel member such as shown in FIG. 2 and that of the channel member of the above-mentioned construction according to the present invention against a side force such as force Fs shown in FIG. 1 acting to bend the channel member in its weakest bending direction will be compared with one another based upon their schematized cross sectional configurations such as shown in FIGS. 4 and 5.
The channel member 100 of FIG. 4 having a cross section schematized from the conventional cross section shown in FIG. 2 comprises a bottom wall portion 102 of a width xe2x80x9caxe2x80x9d and a pair of side wall portions 104 of a depth xe2x80x9cbxe2x80x9d, both having a thickness t1. On the other hand, the channel member 200 of FIG. 5 having a cross section schematized from the above-mentioned channel member according to the present invention comprises a pair of separated bottom wall portions 202 of a width xe2x80x9ca0xe2x80x9d corresponding to the first and second bottom wall portions, a pair of side wall portions 204 of the same depth xe2x80x9cbxe2x80x9d as in FIG. 4 corresponding to the first and second side wall portions, a pair of perpendicular intermediate wall portions 206 of the same depth xe2x80x9cbxe2x80x9d as in FIG. 4 corresponding to the first and second perpendicular intermediate wall portions, and a central wall portion 208 of a width xe2x80x9ca-2a0xe2x80x9d corresponding to the central wall portion, all having a thickness xe2x80x9ct2xe2x80x9d.
For the sake of comparison, the amount of the material constructing the channel members 100 and 200 is assumed to be common for both. Therefore, the following condition must be satisfied:
t1xc2x7(a+2xc2x7b)=t2xc2x7(a+4xc2x7b)xe2x80x83xe2x80x83(1)
Now, taking rectangular coordinates x-y as shown in FIG. 4, the position of the neutral axis Nxe2x80x94N of the cross section of the channel member 100 extending in the flattening direction thereof is determined based upon a balance of the geometrical moment of area on opposite sides thereof, as a displacement y1 from the x-axis, as follows:
t1xc2x7axc2x7(bxe2x88x92y1)=2xc2x7t1xc2x7bxc2x7(y1xe2x88x92b/2)xe2x80x83xe2x80x83(2)
                              ∴                      y            1                          =                                            (                              a                +                b                            )                        ·            b                                a            +                          2              ·              b                                                          (        3        )            
The geometrical moment of inertia I of a beam or column having a rectangular cross section such as shown in FIG. 6 about its neutral axis Nxe2x80x94N passing the center of gravity G of the cross section is provided by a well known formula:                     I        =                              w            ·                          h              3                                12                                    (        4        )            
Further, the geometrical moment of inertia of an optional cross section such as shown in FIG. 7 about an x-axis or a y-axis is calculated from the geometrical moment of inertia of the cross section about an X-axis or a Y-axis passing the center of gravity G of the cross section, the displacement of the X-axis or the Y-axis from the x-axis or the y-axis, respectively, and an area dA of the cross section, as follows:
Ix=IX+x02xc2x7dAxe2x80x83xe2x80x83(5)
Iy=IY+y02xc2x7dAxe2x80x83xe2x80x83(6)
Therefore, the geometrical moment of inertia I1 of the cross section shown in FIG. 5 about its neutral axis Nxe2x80x94N is calculated as follows:                               I          1                =                                            a              ·                              t                1                3                                      12                    +                                    t              1                        ·            a            ·                                          (                                  b                  -                                      y                    1                                                  )                            2                                +                      2            ·                                                            t                  1                                ·                                  b                  3                                            12                                +                      2            ·                          t              1                        ·            b            ·                                          (                                                      y                    1                                    -                                      b                    2                                                  )                            2                                                          (        7        )            
Similarly, taking rectangular coordinates x-y as shown in FIG. 5, the position of the neutral axis Nxe2x80x94N of the cross section of the channel member 200 extending in the flattening direction thereof is determined based upon a balance of the geometrical moment of area on opposite sides thereof, as a displacement y2 from the x-axis, as follows:                                           2            ·                          t              2                        ·                          a              0                        ·                          (                              b                ⁢                                  xe2x80x83                                -                                  xe2x80x83                                ⁢                                  y                  2                                            )                                ⁢                      xe2x80x83                    +                      xe2x80x83                    ⁢                      4            ·                          t              2                        ·            b            ·                          (                                                b                  2                                ⁢                                  xe2x80x83                                -                                  xe2x80x83                                ⁢                                  y                  2                                            )                                      ⁢                  xe2x80x83                =                  xe2x80x83                ⁢                              t            2                    ·                      (                          a              ⁢                              xe2x80x83                            -                              xe2x80x83                            ⁢                              2                ·                                  a                  0                                                      )                    ·                      (                                          y                2                            ⁢                              xe2x80x83                            -                              xe2x80x83                            ⁢                                                t                  2                                2                                      )                                              (        8        )                                          ∴                      y            2                          ⁢                  xe2x80x83                =                  xe2x80x83                ⁢                                            2              ·                              (                                                      a                    0                                    ⁢                                      xe2x80x83                                    +                                      xe2x80x83                                    ⁢                  b                                )                            ·              b                        ⁢                          xe2x80x83                        +                          xe2x80x83                        ⁢                                          t                2                            ·                              (                                                      a                    2                                    ⁢                                      xe2x80x83                                    -                                      xe2x80x83                                    ⁢                                      a                    0                                                  )                                                          a            ⁢                          xe2x80x83                        +                          xe2x80x83                        ⁢                          4              ·              b                                                          (        9        )            
Then the geometrical moment of inertia I2 of the cross section shown in FIG. 5 about its neutral axis Nxe2x80x94N is calculated as follows:                                                                         I                2                            =                              xe2x80x83                            ⁢                                                2                  ·                                                                                    a                        0                                            ·                                              t                        2                        3                                                              12                                                  +                                  2                  ·                                      t                    2                                    ·                                      a                    0                                    ·                                                            (                                              b                        -                                                  y                          2                                                                    )                                        2                                                  +                                                                                                        xe2x80x83                            ⁢                                                4                  ·                                                                                    t                        2                                            ·                                              b                        3                                                              12                                                  +                                  4                  ·                                      t                    2                                    ·                  b                  ·                                                            (                                                                        b                          2                                                -                                                  y                          2                                                                    )                                        2                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          (                                              a                        -                                                  2                          ·                                                      a                            0                                                                                              )                                        ·                                          t                      2                      3                                                        12                                +                                                      t                    2                                    ·                                      (                                          a                      -                                              2                        ·                                                  a                          0                                                                                      )                                    ·                                                            (                                                                        y                          2                                                -                                                                              t                            2                                                    2                                                                    )                                        2                                                                                                          (        10        )            
In evaluating the strength of a beam or column against a bending moment, it is essential to estimate a xe2x80x9cskin bending stressxe2x80x9d, i.e. how much a portion of the cross section remotest from the neutral axis is stressed in tension or compression by the bending moment. The stress at such a portion, when denoted as xe2x80x9c"sgr"xe2x80x9d, is calculated according to the bending moment denoted as xe2x80x9cMxe2x80x9d, the geometrical moment of inertia denoted as xe2x80x9cIxe2x80x9d, and a displacement of the remotest portion from the neutral axis Nxe2x80x94N denoted as xe2x80x9cexe2x80x9d, as follows:                     σ        =                              M            ·            e                    I                                    (        11        )            
The ratio I/e is called a modulus of section. The highest bending stress is evaluated as a ratio of the bending moment M to the modulus of section denoted as xe2x80x9cZxe2x80x9d:                     σ        =                              M            Z                    ⁢                      xe2x80x83                    ⁢                      (                                          wherein                ⁢                                  xe2x80x83                                ⁢                Z                            =                              I                e                                      )                                              (        12        )            
When the modulus of section of a channel member is greater, the skin bending stress is lower for the same bending moment applied thereto.
As an example, when a=80 mm, b=20 mm, a0=15 mm, and t1=3 mm, t2 for satisfying the condition of equation (1) is 2.25 mm, and then y1, y2, I1 and I2 are calculated as follows:
y1=16.7 mm
y2=9.1 mm
I1=12,180 mm4 
I2=21,385 mm4 
In the channel member 100, a portion remotest from the neutral axis N=N is the free ends of the side wall portions 104 displaced from the neutral axis Nxe2x80x94N by a distance equal to y1 (i.e. 16.7 mm), while in the channel member 200, a portion remotest from the neutral axis N=N is, in the case of the above example, the separated bottom wall portions 202 displaced from the neutral axis Nxe2x80x94N by a distance equal to b-y2 (i.e. 10.9 mm). Therefore, denoting the modulus of section of the channel members 100 and 200 with respect to the neutral axis Nxe2x80x94N as Z1 and Z2, respectively,
Z1=729 mm3 
Z2=1,962 mm3 
The ratio of Z2/Z1 is 2.69. Therefore, by using the same amount of material, the maximum skin bending stress will be reduced to less than half by modifying the cross sectional construction of member 100 to that of the member 200, thereby improving the bending strength by more than two times. Further, as well known in the art, the deflection of a beam or column under a bending moment is generally inversely proportional to the geometrical moment of inertia. Therefore, the deflection of the member 200 is nearly half of that of the member 100 under the application of the same side force.
Apart from the comparison of the overall bending strength based upon the geometrical moment of inertia between the normal channel construction of the member 100 and the double-grooved channel construction of the member 200, there is another aspect of improving the strength of a beam or column member against a side force by modifying its cross sectional construction from that of the normal channel member to that of the double-grooved channel member. In the normal channel member, a pair of its free ends in the cross section inevitably form the portion remotest from the neutral axis Nxe2x80x94N of the geometrical moment of area. However, such a free end portion is generally liable to start a breakage of the member at a lower stress. Therefore, it is not desirable that the free ends of the channel member are positioned remote from the neutral axis of the geometrical moment of area. In this regard, the double-grooved channel member according to the present invention can be so constructed that a pair of free ends are positioned close to or even on the neutral axis of the geometrical moment of area, so that the modulus of section of the free ends is made infinite, as will be appreciated with the embodiments of the invention shown and described hereinbelow.
Such an arrangement is available by that the first or second or both perpendicular intermediate wall portions extend substantially twice as much as the first or second or both side wall portions as viewed in the cross section.
For a further detail, the central wall portion may extend substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member.
Further, the first or the second side wall portion or both may also extend substantially in the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, in a sense that the first or the second side wall portion or both may extend to have substantial components of extension in both directions substantially perpendicular to the direction of transverse extension of the elongated wall portion and substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, or in other words, the first or the second side wall portion or both may extend to incline relative to both the direction perpendicular to the direction of transverse extension of the elongated wall portion and the direction parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member. Such a modification will further improve the bending strength of the channel member against a transversely inclined side force.
Further, the first or the second perpendicular intermediate wall portion or both may also extend substantially in the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, in the same sense as in the first and the second side wall portions, such that the perpendicular intermediate wall portions may extend to have substantial components of extension in both directions substantially perpendicular to the direction of transverse extension of the elongated wall portion and substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, or in other words, the first or the second perpendicular intermediate wall portion or both may extend to incline relative to both the direction perpendicular to the direction of transverse extension of the elongated wall portion and the direction parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member. Such a modification will also further improve the bending strength of the channel member against a transversely inclined side force.
Further, the central wall portion may further comprises:
a first roof wall portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the first roof wall portion being connected with the first perpendicular intermediate wall portion along adjacent ends thereof;
a second roof wall portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the second roof wall portion being connected with the second perpendicular intermediate wall portion along adjacent ends thereof;
a third perpendicular intermediate wall portion extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the third perpendicular intermediate wall portion being connected with the first roof wall portion along adjacent ends thereof, so as to define a first inverse sub-channel portion together with the first perpendicular intermediate wall portion and the first roof wall portion;
a fourth perpendicular intermediate wall portion extending substantially perpendicularly to the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the fourth perpendicular intermediate wall portion being connected with the second roof wall portion along adjacent ends thereof, so as to define a second inverse sub-channel portion together with the second perpendicular intermediate wall portion and the second roof wall portion; and
a third bottom wall portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the third bottom wall portion being connected with the third and fourth perpendicular intermediate wall portions along adjacent ends thereof, so as to define a third sub-channel portion together with the third and fourth perpendicular intermediate wall portions. In this case, the channel member will be constructed to be a triply-grooved channel member.
Further, the channel member according to the present invention may further comprise:
a first flange portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the first flange portion being connected with the first side wall portion along adjacent ends thereof, so as to provide a first margin for connection with a cover member; and
a second flange portion extending substantially in parallel with the direction of transverse extension of the elongated wall portion as viewed in the cross section of the channel member, the second flange portion being connected with the second side wall portion along adjacent ends thereof, so as to provide a second margin for connection with the cover member.